Method of preparing thiophenealdehydes



Patented' Jan. 1, 1952 METHODDF PREPARING THIOPHENE- .'ALDEHYDES eWilliam 1S.1-Emerson1and .Tracy-M, Patrck; Jr., -Dayton, Ohio, assignors to Monsanto Chemical 'Company, St. Louis, Mo., a. corporation of Delarwalfe '-No'Drawing. Application Augus'tl'fg 1948,

' '-Seial No. 45,985

.1 v :This inventionrelates Ito-:new :methods of f pre- `paring thiop'henealdehydeseand A:substituted :thiofphenealdehydes. ll/ioreiparticulai'ly, athis inven :tionrrelates to aiinew :method o preparing aan intermediate useful inIthe asynthesislof .sa Wide v.variety of thiophenederivatives.

Thiophenealdehyde has been :prepared by 4a `.variety :of1methods,;but .most of them. are tedious `orzcitherwise objectionable. The mostpracticable methods.involveeither the oxidation of 2-acetothienone ftof.,2-thienyl'glyoxylio acid, followed by decorboxylatiom'or:thezreaction:ofiZethenyl.chloride Ywith hexamethylene tetramine, :but these methods are objectionable sin thatthe lowgyields usually are obtained.

The purpose of this 'invention is to provide a `:new .andziuseful method of preparing vthiophenevaldehydeeandthetaldelcydes :ofvarious substituted ffthiophenes. 5A furtherpurposeof this invention Eisito'provide1a novelmethod of V,preparing high Syiel'ds ofthe .various*thiophenealdehydes.

ifIn accordance with this invention, the thio- .phenealdehydes :are :prepared 'by :reacting thiorphene, nor ;a substituted ithiophene Vwith Nphos- .phorus oxychloride and :an .NN-.disubstituted -iormamidefor examplezdiethyl formamide, .di- :butyl :.formamide, ormpiperidide, N ethyl V,formanilidanor Nfrnethyl-peformtoluidide. Thereaction is preferably conducted under anhydrous l'conditions in solution in a suitable organic solvent, for example V"toluene, 'benzene or Xylene. After the "reagents4- are '.mixed, the resulting solu- `tioniis heated '.toreflux temperatures vfor sufcient time,tor-complete.tlfre'reactiony at vwhich time `the'reaction mass 'is iipoured' into fcold '.Water or ice, andseparated by suitable distillation. An .e'ective :separationmay `be achieved by steam fdistillation, "whereby the "major portion of `the :thiophenealdehydeis coll'ectednzthenonaqueous layer 'ofithe distillate :Aportion of .the thio .phenaldehyde is dissolved in :the V:aqueous layer .and improved -yields 'rare .tachieued iby 'extracting ".thewater solution withttoluene,` orzanoth'er water .-immiscible solvent .zfor 4the thiophenealdehyde Fhenonaqueous Ilayer :and-.the extracts; may then be distilled to separate the thiophenealdehyde.

By this method, ,thiQp-henealdehyde may be prepared in unusually pure state and in very sub- =stantial1yie1`ds- In -addition Ato '.thiop'hene'aldehyde, K :Various substituted thiophenea'ldehydes imayfalso be prepared. LThe useful 'thiophenealdehy'des :prepared in accordance Iwith this in- `vention Fare :represented by the lf'ollowing fstruc- -.tura1 formula:

f2 e `wherein,X.is.a..radca1.ofthegroup consistngo'f .hydrogen,.-halogen and ,alkyl :radicals Suitable ,ha-logensubstituents.incudeiiodinepandfluorine,

salti-rough bromine .and chlorine arevthev mostirnportan-t. .Although .any alkyl V4substituted .thio- .phenea-ldehyde .may .be'lprepared those having Ezample'f'l v-A..1(l00 eml., 3necked ask Ywas provided with an .ecientstirren a thermometer andareflux condenser .sealed .by means ,of a calcium chloride tube. V'Ilhefask Was .charged .with 135 grams o'f N-methylfformanili'de and then, .While .cooling on a -water.bath, .153.4 grams .of v.phosphorus oxy- `chloride was added. iThe Waterbathrwas then .removed and .the `mixture Astirredltor one hour. A solutiono'f 126 gramsofthiophene in' 30G cc. of anhydrous-,toluene was then added and the entire .mass bo'iled ra'treux temperatures 'for one and one-half hours. The reaction mass was then cooled .and `Ypoured .into an equal Avolume of crushed lice. "fThe mixture Was then .steam distille'dan'd the aqueous portion of the condensate `extracted three times with toluene. Theextracts were .then combined with the `nonaqueous. layer of condensate. "The product distilledat `to 86 C. lat 16 mmytotal pressure 'and `was identified 'as '2-thiop11enealdehyde.

Example 2 The -procedure'ofExarnple 1,1Was repeated /except lthat-dimethylformamide 'was vused in place Vrof "the .N-methyl "formanilide LThe Ycompound formed "was f also identified :as12-.thiophenealde- Example :3

The procedure of Example 1 was'repeated"and Y two hours. The final fractionation produced the compound identified as 5-chloro-2-thiophenealdehyde:

The various thiophenealdehydes produced in accordance with the method of this invention are useful intermediates in the preparation, of a Wide variety of organic compounds. The following examples describe in detail various types of reactions by which new and useful chemical compounds are prepared.

Example 5 A solution of 27.5 grams of p-aminophenol in 200 cc. of ethanol and 28.3 grams of 2-thiophenealdehyde were charged to a reaction flask provided with a stirring mechanism and a'reux condenser. The mixture was heated at reflux temperature for fifteen minutes while being' vigorously stirred. The heating'wasthen discontinued and the mixture was stirred for an additional fteenfminutes. Theiiask was then cooled and a crystallineprecipitate was ob- Example 6 A 2-liter, 3-necked ilask was fitted with a stirring device, a thermometer and a reflux condenser. The flask was charged with 40.5 grams of Z-thenal-p-aminophenol, 18 grams of magnesium chips and'750 cc. of anhydrous methanol. The mixture was vigorously stirred and the temperature gradually rose to 32 C. after which it was cooled periodically by immersion in an ice bath. After twenty minutes, the reaction was accelerated and it was necessary to maintain the ask in an ice bath to keep the temperature below 32 C. After one hour, all of the magnesium had dissolved and the reaction mass was then heated and 500 cc. of methanol was evap orated. The residue was then poured in to 50i) cc. of 5 percent aqueous sodium hyroxide while vigorously stirring the reaction mass. During this addition, the flask was immersed in an ice bath. The reaction mass was then diluted With l 250 cc. of 5 percent sodium hydroxide and liltered. The gelatinous mass so separated was mixed with an additional 150 cc. of 5 percent sodium hydroxide and filtered. The combined ltrations and washing were then treated with carbon dioxide and filtered. The filtrate was then cooled and a solid material obtained, which after four successive crystallizations from methanol, was found to have a melting point oi 10'? to 108 C., and was identified as Z-thenyl-paminophenol.

Example 7 4 Point 0f 59 C. was obtained and identied as 2-thenalacetophenone. y v

Example 8 Using the procedure described in the preceding example, except that p-methoxyacetophenone was used in place of the acetophenone, the solid compound so obtained was identiiied as 2-thenal-p-methoxyacetophenone Example 9 A reaction flask was charged with 11.2 grams of thiophenealdehyde, 22.7 grams of 2,4,6-trinitrotoluene, 1 cc. of piperidine and 100 cc. of xylene. The reaction mass was heated at reiiux for fifteen minutes and 1.9 cc. of water was removed from the condensate in a Dean and Stark trap. Upon cooling, the reaction mass `crystallized and was separated by filtration after diluting with 25 cc. of benzene. An additional crop of crystals was obtained by diluting the filtrate with hexane and cooling. The combined precipitates were dissolved in 200 cc.l of benzene, decolorized by heating with activated charcoal, filtered while hot, diluted with an equal volume of hexane, and cooled. An orange colored crystalline solid, thereby obtained, was separated by filtration and dried. The resulting product was identiiied as amixture of the cisand trans-isomers of 1-(2thienyl)2-(2,4,6tri nitrophenyl) ethylene.

Example 10 zolinedione.

Example 11 A reaction flask was charged With 31.3 grams of o-aminothiophenol and 75 cc. of pyridine. The iiask was then charged gradually, While vigorously stirring, with 28 grams of 2-thiophenealdehyde. The mixture was then stirred for onehalf hour at to 95 C., cooled in an ice bath, and acidiiied with dilute hydrochloric acid. An oily substance separated and .soon solidified. `The solid matter was separated by filtration, Washed with water and dried over potassium hydroxide. Three successive crystallizations of the product, from an ethanol solution in an atmosphere of carbon dioxide, produced a substantial yield of a compound identified as 2(2thienyl) -benzothiazoline. i

Example 12 structural formula:

wherein X is a radical of the group consisting of hydrogen, halogen and alkyl radicals, with an N,Ndisuiostituted formamide and phosphorus oxychloride, in an anhydrous medium and separating the resulting product.

2. A method of preparing thiophenealdehyde, which comprises reacting thiophene with an N,Ndisubstituted formamide and phosphorus oxychloride, in an anhydrous solution and separating the resulting product.

3. A method of preparing thiophenealdehyde, which comprises reacting thiophene, in an anhydrous solution, with N-methyl formanilide and phosphorus oxychlorde, and separating the resulting product.

4. A method of preparing 5-methyl-2-thiophenealdehyde, which comprises reacting in an anhydrous solution, Z-methylthiophene with N methyl formanilide and phosphorus oxychloride, and separating the resulting product.

5. A method of preparing 5-chloro-2-thiophenealdehyde, which comprises reacting in an 6 anhydrous solution, 2-chlorothiophene with N- methyl formanilide and phosphorus oxychloride, and separating the resulting product.

WILLIAM S. EMERSON. TRACY M. PATRICK, JR.

REFERENCES CITED The following references are of record in the le of this patent:

v FOREIGN PATENTS Number OTHER REFERENCES Bernthsen and Sudborough: Organic Chemistry, page 549, Van Nostrand, N. Y., 1922 edition.

Whitmore: Organic Chemistry, 884, 893, Van Nostrand, N. Y., 1937.

Richter: Organic Chemistry, pages 649-650, Wiley, N. Y., 1938. f

Alles: J. Pharm. Exp. Ther. 72, 265 (1941).

Seemann: Canadian Journal of Research, v01. 19, sec. B, page 291 (1941) Steinkopf: Die Chemie des Thiophens, page 21, Steinkopf, Dresden, 1941, Edwards Lithoprint 1944.

Powers, `Advancing Fronts in Chemistry, vol. II, page 33, Reinhold Pub. Co., N. Y., 1946.

Williams, Detoxication Mechanisms, pages 194, 197, 198, Wiley, N. Y., 1947.

Caesar and Sachanen: Ind. Eng. Chem. 40, 922 (1948, May).

King and Nord: J. Organic Chem. 13, 635-640 (1948).

Ex parte Bywater and Coleman 83 U. S. P. Q. 4. 

1. A METHOD OF PREPARING A THIOPHENEALDEHYDE, WHICH COMPRISES REACTING A THIOPHENE HAVING THE STRUCTURALFORMULA: 